I have been working on a project which involves short range wifi (2.4+5 GHz) communication. The working distance between antenna and receiver is at most 20 inches. This antenna must also not be so sensitive to external influences (dirty/noisy environment) Antenna and receiver are placed inside an aluminum box which has 40dB attenuation at 5GHz. Also one goal is to limit the directionality of this antenna.

I have tried many things (even using a paperclip or short or long peices of wire. Have found some success with longer wires (in the range of 8-10 inches). The main problem I have at the moment is my SNR is very high (90+dB) but when i try and run bandwidth I am getting very low data rates.

The problem with the data rate of your wireless link might be due to large amounts of reflection or resonances inside your metal box. You might want to try adding absorber to the walls of the box.

If you don't absolutely need an antenna - if its only 20 inches and you want to be protected from external influences (if the interferers are also inside the box), just use a coaxial connection between transmitter and receiver. You could also just avoid RF entirely and just connect the two devices with serial data communication (USB, I2C, Ethernet, etc.).

Hi...i am a new user here. I had the same question. I think you should use a paper clip, it is small and won't have much directivity.It seems you are in a shield box so noise doesn't matter, and antennas don't filter noise anyway.